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Pontiac Trans Am SD-455: Did Pontiac Save its Best Muscle Car for Last?

HOT ROD logo HOT ROD 5/19/2017 Hot Rod Network Staff

1974-pontiac-trans-am-super-duty-front-three-quarter Pontiac Trans Am SD-455: Did Pontiac Save its Best Muscle Car for Last? It was over, Johnny. The muscle car thing had run its fun, psychedelic course by the early 1970s. Rising insurance rates, falling compression ratios, and looming federal regulations effectively killed the fun like your junior high principal turning on the gymnasium lights at the end of the eighth-grade dance. Time to go.

Pontiac lingered as long as possible, and the Super Duty 455 engine was the final song they got the DJ to play as everyone shuffled off the floor.

That the SD-455 was produced at all was a miracle, given how quickly high-performance became politically incorrect by the early 1970s. Installing it in the Firebird was another challenge because the F-Body line was very nearly canceled after 1972. Sales for ponycars dropped precipitously as younger buyers sought more fuel-efficient cars. Consequently, Firebird sales plunged more than 56 percent between 1971 and 1972, to less than 30,000. Only 1,286 of them were Trans Ams.

Fortunately Pontiac was filled with passionate people, and they pushed the Super Duty 455 project along. It helped that the engineers were deep into the project when the market turned against high-performance cars, so it seemingly wouldn't take much to push the SD-455 over the line.

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Pontiac introduced the engine to the press in the summer of 1972, during the brand's annual model line preview. Unsurprisingly, the response was enthusiastic. There was much to be excited about.

Almost every element of the engine was unique, from the block and heads to the rotating assembly, intake manifold, carb, and more. It was announced at the introduction with a 310hp rating, along with plans to make it available at the start of the 1973 model year. That didn't happen. Creative interpretation on Pontiac's part of EPA's emissions test for certification didn't go as planned, which pushed back production.

By the time Pontiac recertified the engine, with a revised camshaft and commensurate carburetor adjustments, the horsepower rating was revised down to 290. It was the spring of 1973, but the cars didn't roll off the line in meaningful numbers, creating a significant customer relations problem. The company had stacks of preorders for cars it couldn't deliver. By the end of 1973 only 295 Super Duty-powered Firebird models had been built: 252 Trans Ams and 43 Formulas.

The engine added $521 to the bottom line for a Trans Am and $675 for a Formula. A four-speed manual transmission was standard, and the stout Turbo 400 three-speed automatic was optional. Air conditioning was available with the automatic transmission, but that pushed the rear axle ratio up to 3.08. Non-A/C cars received a shorter 3.42 gearset.

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There was plenty of confusion about the horsepower rating. Before the Internet the only reference data most enthusiasts had were six-month-old magazines promising 310 horses. Nevertheless, when the SD-455 finally hit the street, praise for it was universal, especially when it turned mid- and high-13-second e.t.'s at a time when a new big-block Corvette generally required another full second to run the quarter-mile.

It was great performance indeed for a 3,800-pound Firebird with smog equipment and a compression ratio of only 8.4:1, but the 395 lb-ft of torque and the exceptional airflow of the special cylinder heads more than offset the mandated handicaps. Even down a few horsepower, thanks to a "smaller" camshaft than the original spec, the production model was the quickest car out of Detroit in years.

The end for the SD-455 came too quickly for enthusiasts. With catalytic converters on the docket for 1975 and other related emissions changes, Pontiac knew from the very start the engine wouldn't live beyond 1974, but it was a hell of a ride while it lasted.

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Ironically, the enthusiasm for the engine wasn't matched by sales. The delayed release in 1973 certainly squeezed the production run in the first year, but only 1,001 additional SD-powered cars were built in 1974, bringing the two-year total to 1,296. Cost was a likely factor, as the $521 premium for the Trans Am was the equivalent of more than a $3,700 option in today's money, adjusted for inflation. And that was actually a premium on the already extra-cost 250hp 455 engine, which made the true cost more like $700 over a base Trans Am model. Some dealers also charged more because of the car's scarcity. Bottom line: 13-second e.t.'s from the factory didn't come cheap.

Collector John Nikolas was too young to drive when the Super Duty 455 finally hit the street, but his neighbor drove a 1974 Buccaneer Red example as a company car. His company happened to be General Motors and the neighbor happened to be Pontiac general manager Martin J. Caserio.

"I always admired the cars he'd bring home, including early Firebird Formulas that would chirp Second gear going up his winding driveway," says Nikolas. "But it was that red Super Duty car that really stuck with me. I knew I had to have one someday."

Today Nikolas owns four SD-455 Trans Ams, a white 1973 model and three from 1974, including the Cameo White example profiled here. A 51,000-mile car he purchased in 2004, it was sold originally in Texas and filtered through a few owners, including a well-known collector in the SD-455 world who owned 19 of them at one time, before ending up in a quiet area of western Michigan.

"The car was listed online for a long time, but it was located kind of far away from everywhere," says Nikolas. "I was apparently the only one who drove all the way out there to check it out in person and bought it on the spot."

The previous owners all took excellent care of the car. It was never modified, and every original component that was replaced over the years for maintenance or repair was never thrown away. Nikolas has them all in a box.

It's a very well-equipped Trans Am, too, with the Custom interior that included a specific "horse collar" seat upholstery design with detailed piping, specific door panel trim, and a grab handle on the dashboard. The car also features power windows, power locks, air conditioning, and more, a collection of options that helped push the sticker price to nearly $6,300. That slower 1974 big-block Corvette cost about the same.

Nikolas purchased the car with the intent of a concours restoration, which he'd recently completed on his 1973 Trans Am, but the plan changed as he continued to enjoy the remarkably unmolested car.

"It's a great driver with a lot of torque on tap," he says. "Just jump in and go. I drive it to work regularly and take it cruising on Woodward Avenue in the summer. I've driven it on a couple of the Hot Rod Power Tours. It has never let me down."

Although it hasn't been restored, it was repainted sometime in the late 1970s, which was all too common for cars of the era, especially in climates such as Texas where the sun is unrelentingly punishing on thin factory paint jobs. It also has a new headliner and some light upholstery work accomplished with N.O.S. material that came with the car.

One more thing: The iconic shaker scoop has been opened up to feed fresh air into the Quadrajet carburetor. When introduced in 1970, the shaker was a functional fresh-air inlet, but Pontiac capped it off in 1973 for noise reduction. Perhaps anticipating owners' actions, the scoop was sealed with a simple plate held in place with only a trio of easily defeated rivets.

"Between the performance and the mystique surrounding the engine, there's really something magical about these cars," says Nikolas. "They not only represent the last of the true muscle cars, but the sort of confident, no-holds-barred engineering that really made Detroit great."

At a Glance

1974 Trans AM SD-455

Owned by: John Nikolas

Restored by: Unrestored (1970s repaint)

Engine: 455ci/290hp LS2-code Super Duty 455

Transmission: Turbo 400 automatic

Rearend: 10-bolt with 3.08 gears

Interior: Custom "horse collar" vinyl bucket seats

Wheels: 15x7 Honeycomb

Tires: 225/70R15 BFGoodrich Radial TA

Special parts: One of only 943 SD-455 Trans Am models built in 1974

15 Facts You Didn't Know About the SD-455

The Super Duty 455's production run may have been brief, but it left an indelible mark on muscle car history. Between Pontiac's ambitions and the hardware that tied it all together, there's plenty to learn about the SD-455. We have collected the most important elements to put casual enthusiasts in the know.

It's All in the VIN

The first step in verifying an authentic SD-455 Trans Am or Formula is checking the vehicle's VIN. The fifth character will be an X, the engine code. "Regular" 455 engines had a Y code in 1973 and 1974.

Restricted Duty

The SD-455 was originally scheduled to be offered in several Pontiac models, including the Grand Prix and Le Mans/GTO. The EPA-driven production delays squashed those plans, as Pontiac focused on certifying the engine solely for the F-Body platform. That didn't stop one magazine, however, from prematurely declaring the Super Dutypowered 1973 GTO its Car of the Year.

Cam Change

The original camshaft for the SD-455 had the same profile as Pontiac's Ram Air IV engine, which is commonly known as the 041 camshaft (for its original part number). To satisfy the EPA's emission test, the camshaft was changed to the specs of the manual-transmission Ram Air III, aka the 744. It brought horsepower down from 310 to 290.

Short Supply

Enthusiasts quickly learned that the SD-455 packed some stout internals, including forged steel rods with larger, stronger bolts. Dealers were quickly flooded with service parts orders. At one point there were 1,350 back orders for the rods when only 295 SD-455 cars had been built by the end of 1973. Pontiac clamped down and insisted VINs accompany orders for the special parts.

A Better Block

The SD-455 block was unique, featuring four-bolt main caps—a feature shared only with the 1971-172 455 H.O.—cast-in provisions for dry-sump oiling, beefier bulkheads, reinforcing valley ribs, and screw-in galley plugs. The hole for the distributor was larger, too, to accommodate a larger drive gear than what was used on "standard" distributors.

Block Codes

Like other Pontiac engines, the SD-455 block was stamped with a code that delineated its specific usage. Located on the front of the block, toward the deck on the passenger-side cylinder blank, were four SD-specific codes: ZJ (1973 manual), XD (1973 automatic), W8 (1974 manual), and Y8 (1974 automatic).

Head's Up

Much of the Super Duty 455's performance advantage lies all in the special round-port, open-chamber cylinder heads, which were developed in conjunction with aftermarket experts AirFlow Research. You can spot them at a glance with the "16" designation over the center exhaust ports.

One-of-a-Kind Q-Jet

A specific Q-jet carburetor was used on the SD-455, which was visually distinguished by a slanted, or slash-cut, vent tube at the front. Other Pontiac engines' carbs had completely vertical tubes. There were four carb ID numbers for the SD engines: 7043273 (1973 manual), 7043270 (1973 automatic), 7044273 (1974 manual), and 7044270 (1974 automatic).

Oil Pump Problems

An 80-psi oil pump was unique to the SD-455, and it generated too much pressure for the engine, particularly when cold, which proved damaging for some engines. Replacing it with the conventional 60-psi pump used in other Pontiac engines is the recommended fix. The SD pump is shown here at left with a conventional 60-psi pump. It is identifiable by the longer, removable cover for the internal spring, located just above the pickup tube.

Intake Manifolds

Intake manifolds differed between 1973 and 1974. The 1973 SD-455 intake manifold has an "LS2" casting on the right-front corner, while the 1974 unit shows "LS2 X" in the same area.

Hairy Air Intake

The original air intake hose was made of a fabriclike material that looked like hair. Aftermarket replacement hoses have an incorrect smooth appearance. It's the same with other Trans Am models of the era, too.

Down Under Find

In 2012, Australian Michael Scicluna purchased what he believed was a garden-variety 455-powered 1973 Trans Am in need of restoration. It had been in Australia since 1981 and was converted to right-hand drive. Turns out it was the original SD-455 test vehicle Pontiac loaned to automotive media. Expert Rocky Rotella helped authenticate the car, which Scicluna plans to restore.

Chicago Show Car

At the 1974 Chicago Auto Show, Pontiac showed a very unique black-and-gold Super Duty Trans Am. It was a 1973 model that served as an internal design concept for the Screaming Chicken hood graphic and was updated with 1974 styling. It also clearly previewed the cues that would be introduced two years later on the 1976 Trans Am's Pontiac 50th Anniversary special edition.

Exhausting Info

Super Duty cars featured a specific 2 1/2-inch system, and the 1973 model was unique for twin resonators ahead of the transversely mounted muffler. They were not included on 1974 models.

Formula Shaker

Super Dutyequipped Firebird Formula models were unique with their shaker scoop. After the engine's production delay, it was cheaper and faster for Pontiac to use the Trans Am hood and shaker scoop with the SD-455 than certifying it with the Formula air induction system.

Author Barry Kluczyk delivers more on the Super Duty Trans Am and Formula models in his new book from CarTech. It is the sixth in the publishing companies In Detail series and offers the history of how the SD-455 models came to market, as well as an inside look at the unique engine, design details, and more. More information is available at cartechbooks.com; buy at amazon.com, bn.com, and other retailers.


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